This invention relates to a wire-terminal connecting method in which a wire for feeding a power source current or a signal current to an on-vehicle part is connected to a terminal by ultrasonic welding.
One known related wire-terminal connecting method is disclosed in JP-A-54-43588.
As shown in FIG. 7, this related wire-terminal connecting method is directed to the method of an invention in which a distal end portion 51a of a wire 51 is beforehand fixed into a semi-circular shape, and thereafter this fixed distal end portion 51a, together with a flat-type aluminum wire 55 (serving as a connecting wire), is held between a tip 59 and an anvil 60 of an ultrasonic welding machine 56, and an interface 65 (FIG. 8) of joining between the wire 51 and the flat-type aluminum wire 55 is heated and melted by vibrational energy, thereby effecting the welding.
The distal end portion 51a of the wire 51 is fixed into the predetermined shape by the use of a resistance welding machine (not shown) including an upper electrode with a semi-circular fitting groove and a lower electrode disposed in opposed relation to this upper electrode.
In FIG. 7, reference numeral 55 denotes the flat-type aluminum wire to be connected to the wire 51, reference numeral 56 denotes the ultrasonic welding machine, reference numeral 57 denotes an ultrasonic wave-generating source, reference numeral 58 denotes a horn for transmitting ultrasonic waves from the ultrasonic wave-generating source 57, and reference numeral 59 denotes the tip provided at a distal end of the horn 58.
The tip 59 has a semicircular groove 59a extending in a direction perpendicular to a direction a of vibration of ultrasonic waves. Reference numeral 60 denotes the anvil provided in opposed relation to the tip 59. An upper surface of the anvil 60 is formed into a flat surface.
The flat-type aluminum wire 55 and the wire 51 are placed on the anvil 60 of the ultrasonic welding machine 56 in such a manner that the wire 51 is superposed on the aluminum wire 55, and then the tip 59 is moved toward the anvil 60, so that the distal end portion 51a of the wire 51 fits into the groove 59a in the tip 59. As a result, the wire 51 is pressed from the upper side, and is held in place since the depth of the groove 59a in the tip 59 is slightly smaller than the height of the semi-circular distal end portion 51a of the wire 51.
Then, when ultrasonic waves are applied from the ultrasonic wave-generating source 57 via the horn 58 and the tip 59, the vibrational energy propagates to the interface 65 of joining between the wire 51 and the flat-type aluminum wire 55 while the wire 51 is kept in a restrained condition since the direction of extending of the groove 59a in the tip 59 is substantially perpendicular to the vibrating direction a. As a result, this joining interface portion 65 is heated and melted by frictional heat, thereby connecting the wire 51 and the flat-type aluminum wire 55 together.
However, the above related wire-terminal connecting method has the following problems to be solved.
Firstly, when the wire (workpiece) 51 is pressed by the tip 59 as shown in FIG. 8, stresses concentration a boundary portion 51b between each edge portion 59b of the tip 59 and the wire 51, and besides when the tip 59 is ultrasonically vibrated, the edge portion 59b of the tip 59 and the wire 51 rub against each other at each boundary portion 51b, thus inviting a problem that wire elements 51c undergo damage such as cutting.
Secondly, the larger the pressing force, applied by the tip 59, is, and the higher the ultrasonic vibration frequency is, the shorter the time of heating and melting of the joining interface portion 65 is, and on the other hand there is encountered a problem that the plurality of wire elements 51c are more liable to become loose, and also are more liable to undergo damage such as cutting. Therefore, it has been desired to provide an ultrasonic connecting method in which even when the ultrasonic vibration frequency is high, the wire elements 51c will not undergo damage such as cutting, and the operation for connecting the wire 51 and the flat-type aluminum wire 55 together can be effected easily.
And besides, when a conductor portion of a thick wire (connected to a battery so as to supply a source current) or a conductor portion of a thin wire (connected to an on-vehicle part so as to feed a signal current) is kept in an exposed condition, waterdrops, dust and so on deposit on the conductor portion (conducting portion), which invites a problem that the performance of contact between the conductor portion and the terminal is lowered.